Life History and Development

Chapter 3 Life History and Development Oldrich Nedv eˇ d 1 and Alois Hon eˇ k 2 1 Faculty of Science, University of South Bohemia and Institute of Entomology, Academy of Sciences, CZ 37005 Cˇ esk é Bud eˇ jovice, Czech Republic 2 Department of Entomology, Crop Research Institute, CZ 16106 Prague 6, Czech Republic Ecology and Behaviour of the Ladybird Beetles (Coccinellidae), First Edition. Edited by I. Hodek, H.F. van Emden, A. Honeˇk. © 2012 Blackwell Publishing Ltd. Published 2012 by Blackwell Publishing Ltd. 54 3.1 INTRODUCTION from spermatheca (receptaculum seminis) can enter during oviposition, and for oxygen diffusion. A. bipunc- Coccinellids are holometabolous , i.e. they have a tata possesses 40 – 50 pores in two rings, Platynaspis ‘ complete metamorphosis ’ , and pass through the fol- luteorubra have clusters of pores at both ends of the lowing stages: egg, larva, pupa and adult. Egg stage egg. Chilocorini have trumpet shaped structures lasts 15 – 20% of the total preimaginal developmental besides the tube like micropyles (Ricci & Stella 1988 ). time, larva 55 – 65% and pupa 20 – 25% (Hon eˇ k & The egg of Scymnus sinuanodulus has a rosette of 4 – 11 Kocourek 1990 , Dixon 2000 ). cup - shaped and 13 – 20 semicircular structures that are like micropyles (Lu et al. 2002 ). The surface of the coccinellid egg ( chorion , egg 3.2 EGG shell) is usually smooth, except for the eggs of Epil- achninae which bear a polygonal sculpture (Klaus- 3.2.1 Egg morphology nitzer 1969b ; Fig. 3.1 c), and Rhyzobius with a granular surface (Ricci & Stella 1988 ). The smooth surface Coccinellid eggs are usually elongate, oval or elliptic. may be soaked with an oily excretion provided by They vary in colour from almost transparent ( Scymnus accessory glands of the mother. The excretion is col- louisianae ; Brown et al. 2003 ), light grey ( Stethorus ), ourless, or rarely red (as in Calvia quatuordecimguttata ; yellowish ( Halyzia ) through bright yellow (most Klausnitzer & Klausnitzer 1986 ) and contains defen- species) to dark orange (Chilocorini), sometimes green- sive or signalling alkanes (Hemptinne et al. 2000 ; ish (Klausnitzer 1969b ). They are laid either upright, Chapter 9 .). attached (glued) to the substrate by the lower end (Coc- The yolk of the egg contains many nutrients . cinellinae) or lying on their side (Scymninae, Coccid- During embryonic development of the A. bipunctata ulinae, Chilocorinae). The ‘ upper ’ or anterior pole egg mass, lipid and glycogen contents decline strongly, bears a ring of micropyles (Fig. 3.1 ) – pores in the while egg protein decline more slowly. Free carbohy- chorion (the egg shell) through which spermatozoa drates decline early in egg development and increase (a) (b) (c) (d) Figure 3.1 SEM photographs of ladybird eggs. (a, b) Harmonia axyridis , (c, d) Cynegetis impunctata. (a, c) upper parts of eggs with ring of micropyle openings; (b) ring of micropyles; (d) detail of a micropyle opening. 56 O. Nedveˇ d and A. Honeˇk before hatching (Sloggett & Lorenz 2008 ). Energy per microlitres may be calculated as: V = L W 2π /6, where L unit egg mass is lowest in the generalist A. bipunctata , is length and W is the width of the egg (Takakura which also has relatively large eggs, and is highest in 2004 ). the specialized Anisosticta novemdecimpunctata , which The weight of the eggs of large species C. septem- has small eggs. punctata (15.4 mg adult dry mass) and small species A few days or hours before hatching the eggs become P. quatuordecimpunctata (3.7 mg adult dry mass) dif- greyish, because the larvae are visible through the fered little (0.20 versus 0.18 mg) (Hon eˇ k et al. 2008 ). chorion. The fi rst instar larvae of Coccinellinae and C. septempunctata produces a larger number of indi- Epilachninae may possess special structures on head vidually smaller eggs than C. transversoguttata (Kajita and prothorax called egg teeth which probably help et al. 2009 ) which has the same body size. Similarly, the larva in hatching. Hatched larvae rest some time Har. axyridis produces larger egg clusters with smaller on the empty egg shells, and may eat them. eggs (0.28 mm 3 ) than Har. yedoensis (0.36 mm 3 ) Ladybird eggs are defended chemically against pre- (Osawa & Ohashi 2008 ). Species of similar adult size dation, including that which is intra - guild, and they laying smaller eggs may incur higher costs per unit are suitable to varying degrees as food for other lady- mass than species laying larger eggs. More specialized birds (Rieder et al. 2008 ; Chapter 7 ). species reproducing at lower aphid densities may provide neonate larvae with more nutrients to facili- tate the fi nding of an aphid colony (Sloggett & Lorenz 3.2.2 Egg size 2008 ). The fi tness of young larvae is positively related to Insect species have a genetically fi xed maximum egg size. Starving fi rst instar larvae survived substan- number of ovarioles related to egg cluster size (see tially longer (using only each individual ’ s yolk below) and/or a fi xed maximum size of each single reserves ) in large Coelophora bissellata (with egg egg – traits expressed with ample food and other volume 1.53 mm 3 ) than did three other Malayan favourable environmental conditions. With a limited species with egg volumes of 0.81 – 1.20 mm 3 (Ng food supply, the size of eggs may be reduced and their 1988 ). However, small eggs have a higher rate of number maintained, or decreased and their size embryonic development , which decreases the risk maintained. Coccinellids adopt the second strategy of egg predation (Majerus 1994 ). Developmental time (Stewart et a1. 1991a, b ; Dixon & Guo 1993 ; see was 3.0 days in Har. yedoensis possessing larger eggs also 5.2.3 ). This is similar to birds, for example, where and 2.7 days in Har. axyridis with smaller eggs (Osawa egg weight ( E ) across species increases in direct pro- & Ohashi 2008 ). There is a strong selection pressure portion (almost isometrically) to body weight ( W ) on fast development and hatching synchrony in can- of the female and inversely to the ovariole number nibalistic ladybirds. Minimum egg size is, however, (O ): log E = 0.83 · log( W / O ) − 0.44 (Stewart et al. constrained by the minimum size at which fi rst instar 1991b ). larvae can fi nd (by extended walking) and kill prey The size of eggs is thus related to the average body (Stewart et al. 1991b ). size of the species; it is less than 0.4 mm in the smallest Small inter - individual variation in egg size was genera and over 2 mm in the largest genera. Eggs of reported in Har. axyridis : mean egg mass was 0.246 mg, Scymnus louisianae are 0.5 mm long and 0.2 mm wide with the minimum average in offspring of individual (Brown et al. 2003 ). Adult Clitostethus oculatus are females 0.196 and the maximum 0.278 (Prevolsek & only 1.26 mm long and the eggs are 0.41 mm long and Williams 2006 ). About 30 small eggs were laid com- 0.18 mm wide, greenish to yellowish - white, with a pared with only about 20 large eggs. Intra - individual reticulate chorion; whereas adult Delphastus pusillus variation in egg size with varying food levels was are 1.39 mm long, the eggs are 0.43 mm long and minimal. 0.23 mm wide, white and smooth (Liu & Stansly 1996a ). Eggs of Stethorus pusillus are 0.4 mm long, eggs of A. bipunctata 1.0 mm long, eggs of C. septem- 3.2.3 Cluster size punctata 1.3 mm long, eggs of Henosepilachna argus 1.7 mm long, and eggs of Anatis ocellata 2.0 mm long Eggs are either laid singly (Scymninae, Coccidulinae, (Klausnitzer & Klausnitzer 1986 ). Egg volume (V) in Chilocorinae – mostly coccidophagous groups) or in Life history and development 57 clusters ( batch , clutch – Coccinellinae – aphidopha- may have been underestimated, because some of them gous, Epilachninae – phytophagous) (Klausnitzer & had been emptied recently, therefore had not developed Klausnitzer 1986 ). There are a few exceptions. In a second large maturing oocyte, and thus were Chilocorinae, the coccidophagous Orcus chalybeus lay overlooked. eggs in clusters (Thompson 1951 ); Exochomus quadri- In interspecifi c comparisons, there is a general linear pustulatus usually lay their eggs in small groups but correlation between the number of ovarioles and the sometimes also individually (Sengonca & Arnold cluster size (Dixon & Guo 1993 ). However, adult size is 2003 ). Within Coccinellinae, Synonycha grandis lay strongly determined by food availability during previ- sparse clusters with the eggs a few millimetres apart; ous larval development (Rhamhalinghan 1985 ) while Megalocaria dilatata lay eggs in two rows (Iablokoff - cluster size is affected by food availability during the Khnzorian 1982 ). In the adelgid eating specialist development of oocytes. Oocyte development and Aphidecta obliterata , 20% of ‘ clusters ’ contain a single maturation takes a few days and there are several egg, and a maximum cluster size observed on spruce oocytes of different stages in each ovariole sequentially needles was fi ve eggs (Timms & Leather 2007 ). ordered in chambers or follicles , so that the female is The eggs in clusters of Coccinellinae are typically able to lay a full clutch of eggs from both ovaries daily. tightly packed in an upright position. The cluster size The total egg load is usually split into two or more is anatomically determined by the number of ovari- clusters. It is uncertain whether eggs of such small oles ( 3.5.5 ), which is similar in the left and right clusters come from one ovary only, or from a combina- ovaries. The usual number of eggs per cluster in tion of both. optimal conditions is equal to about half of the total Fois and colleagues (unpublished) found 5 – 72 eggs ovariole number.

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